1. Field of the Invention
This invention is in the field of traffic control systems in which command signals from a traffic controller are applied to load switches to control the energization of traffic signal lights to regulate the flow of traffic. More particularly, this invention relates to a recorder of key operational information of the traffic control system which visually displays this operational data. Included in the key operational information recorded is the state of the command signals and of the energization of the traffic signal lights when an error in the operation of the systems is detected, which information is an aid identifying the sources, or causes of errors and, thus, in correcting them.
2. Description of the Prior Art
The use of traffic signal lights to control the flow of traffic, particularly at the intersection of two or more streets or highways, is well known. The traffic signal lights controlling traffic at one intersection are typically controlled by a local traffic controller which is programmed to produce command signals which are applied to load switches. The load switches in turn energize and deenergize, or turn on and turn off, traffic signal lights of the system. Typically, one load switch controls one or more traffic lights which are connected in parallel with a source of electrical power, normally AC. The lights controlling a flow of traffic on one street (single phase traffic) are grouped together physically and logically. As a typical minimum, such a group of lights would consist of a single traffic signal head with one red, one yellow, and one green signal light for controlling traffic coming from a single direction, and would most likely include a second red, yellow and green signal lights coupled in parallel with the first red, yellow and green signal lights for controlling traffic coming from an opposite direction. Obviously, other types of lights for controlling left turns, right turns, pedestrian traffic, etc. can also be included, and if they are, there would be a separate load switch for each such type. In the typical minimum configuration, one load switch would be associated with each of the red, yellow and green lights of a single traffic head, and the load switches for one signal head would constitute a group, or block, of such switches.
The relevant prior art has been primarily concerned with detecting malfunctions of the traffic controllers of such systems examples of which would be issuing conflicting command signals, and in the energizing of traffic signal lights such as energizing a traffic signal light in the absence of a command signal from the controller.
In addition, U.S. Pat. No. 4,135,145 which issued on Jan. 16, 1979 and is entitled "Error Detecting Circuit For A Traffic Control System", teaches an error detection circuit for a traffic control system that is electrically connected to traffic signal light energizing circuits for turning on and off the traffic signal lights controlling the flow of a single phase of traffic. The error detector circuit of this invention senses the operating states of the traffic signal lights controlled by a single block of load switches and produces an error signal if certain relationships between the energization status of such lights exists for more than a predetermined period of time. The error signal, when produced, is applied to a latch circuit which in turn causes a visual indicator to be energized and remain energized. The visual indicator identifies to a serviceman the group of traffic signal lights and their associated block of load switches which were the source of the error. As the complexity of the traffic control systems increases, which result in the number of load switches and signal lights to be controlled by such load switches increases, there is a need for better diagnostic tools to aid a serviceman in identifying the cause of errors detected by the system's fault detectors so that the system can be restored to its normal operating mode as quickly as possible.